CMOS Voltage Reference Circuit With Dual Feedback at Low Supply Voltage

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Solution Overview

Problem

Existing voltage reference circuits face challenges in achieving high precision and robustness, especially at low supply voltages (below 1.0V) and in the absence of bipolar junction transistors (BJTs), due to sensitivity to noise, leakage currents, and manufacturing spread.

Innovation Solution

A voltage reference circuit based on CMOS technology, utilizing two asymmetric differential amplifiers with transistors having different threshold voltages and a resistor string with separate feedback loops to provide a reference voltage, achieving temperature and process spread compensation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional bandgap reference circuits are used, then high precision reference voltage can be achieved, but they cannot operate at low supply voltages below 0.9V

Engineering Contradiction:

Improvereference voltage precisionVSAvoidsupply voltage requirement

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent replaces bipolar junction transistors (mechanical/physical structure requiring specific voltage headroom) with CMOS transistors operating in sub-threshold region, enabling operation at supply voltages below 0.9V while maintaining reference precision through feedback control

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operating parameters of MOS transistors to operate in sub-threshold region with specific width-to-length ratios, allowing the circuit to function at ultra-low supply voltages while generating the required reference voltage through controlled current densities

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If open-loop voltage reference circuits are used, then circuit complexity is reduced, but precision and performance deteriorate due to sensitivity to noise and leakage

Engineering Contradiction:

Improvecircuit architecture complexityVSAvoidreference voltage precision

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent implements a closed-loop feedback architecture where the reference voltage output is fed back to control the operating points of differential amplifiers, automatically compensating for noise, leakage currents, and device variations to maintain high precision

Inventive Principle:

Principle #23Feedback

3Ease of manufacture

If bipolar junction transistors are used, then reference voltage generation is simplified, but the circuit cannot be implemented in pure CMOS technology

Engineering Contradiction:

Improveimplementation simplicityVSAvoidCMOS technology compatibility

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The patent substitutes bipolar junction transistors with MOS transistors operating in sub-threshold region, enabling pure CMOS implementation while achieving equivalent or superior performance through controlled threshold voltage effects and feedback mechanisms

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Stability of the object's composition

If transistors with matched threshold voltages are used, then circuit symmetry is improved, but temperature and process spread compensation capability is reduced

Engineering Contradiction:

Improvecircuit symmetryVSAvoidtemperature and process compensation

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent deliberately uses asymmetric transistor pairs with different width-to-length ratios in differential amplifiers, creating controlled asymmetry that generates complementary temperature coefficients to compensate for process variations and improve reliability across temperature ranges

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentUS20250147536A1Voltage reference circuit, integrated circuit, and method for generating a reference voltage

Publication Date: 2025.05.08 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

AI summary

In an embodiment a voltage reference circuit includes a first asymmetric differential amplifier and a second asymmetric differential amplifier, each having two transistors with different threshold voltages as a differential pair and a resistor string arranged between an output of the first asymmetric differential amplifier and a supply terminal, the resistor string including a first portion, a second portion and a connecting circuit node interposed between them, wherein an output of the second asymmetric differential amplifier is coupled to the connecting circuit node, wherein the first portion of the resistor string is configured to provide a first feedback voltage that is fed back to input terminals of the first asymmetric differential amplifier, and the second portion of the resistor string is configured to provide a second feedback voltage that is fed back to input terminals of the second asymmetric differential amplifier, and wherein the voltage reference circuit is configured to provide a reference voltage at the output of the first or the second asymmetric differential amplifier.